 Good day everybody. This is Dr. Sajja Sanyal, Professor of the Department Chair. This is going to be a static demonstration of certain desiccant specimens of the spinal cord. So we have removed the occipital bone from here. This is a prone cadaver. We have done a posterior fossa craniectomy. So we have removed the floor of the posterior fossa. Then we continued down. We removed the laminate of the cervical vertebrae from the cervical thoracic lumbar sacral coccygeal. And we also removed the paraspinal muscles. And thereafter, we have split the dura to show the spinal cord. In an earlier section, we had mentioned the upper part of the spinal cord and the spinal nerve roots and many other features here. Now we shall focus on this region. That is the junction between the medulla and the cervical spinal cord, the cervical medullary junction. So let's start off with this portion here that we can see, this region. So this is a highly analyzed view of the same thing. And we can see that this is the one cerebellar hemisphere. This is the other cerebellar hemisphere of the same prone cadaver. And in between, we can see the cerebellar vertebrae. So as I mentioned, we have removed the occipital bone, the squamous part of the occipital bone. So therefore, the foremen magnum has also been removed in the process. We notice essentially two things which I want to highlight. One is we can see this big structure here. This is a highly analyzed view of the left vertebral artery. This portion of the vertebral artery is V3, the third part of the suboccipital part of the vertebral artery. Why is it called the suboccipital part? Because the vertebral artery in this portion, it arches over the posterior to the atlus and it enters into the suboccipital triangle, which I shall mention just now. And then it pierces through the floor of the triangle and it enters into the cranial cavity through the foremen magnum and it becomes the fourth part that is the intracranial part of the vertebral artery. So this is the vertebral artery. What is the suboccipital triangle that we mentioned just now? The suboccipital triangle is located under the occipital bone and there are two such triangles, one on either side of the midline. So one barge of the triangle is like this approximately. This is the supramedial margin. Then we have another margin of the triangle which runs like this. This is the supralateral margin and there is another margin which is like this which is called the infrolateral margin. The supramedial margin is formed by the rectus capitus posterior major and next to that is the rectus capitus posterior minor. These are all very small muscles under the occipital bone. The supralateral margin is formed by the superior oblique muscle of the head and the infrolateral margin is formed by the inferior oblique muscle of the head. The roof of the triangle is formed by the semi-spalentis capitus muscle and the floor is formed by the posterior to the atlas which has been removed and the posterior to the occipital membrane and the content of the triangle, the most important content is this one here. This is the vertebral artery which I mentioned. It arches over the posterior to the atlas, pierces through the floor that is the posterior to the occipital membrane and it enters into the cranial cavity. The other content of the triangle is the suboccipital nerve which is the dorsal ramus of C1 which supplies these structures here. A few quick words about this part of the vertebral artery, the third part. The third part of the vertebral artery, it gives a few small branches to the muscles in this region and after that it enters into the cranial cavity where it supplies the posterior circulation of the brain. Now let's mention a few quick words about this portion of the cerebellum that we can see here. This portion cerebellum is the midline portion is called the vermis and in this region got an enlarged portion that is called the cerebellar tonsil. When there is a supra-tentorial compression like for example from an extradural hematoma pressing down on the brain, this cerebellar tonsil tends to push down with the medulla through the foremen magnum and reduces the condition which on MRI it looks like a cone and therefore it refers to as a medullary coning which is a very serious condition and it can compress the vital cardiorespiratory centers of the medulla and can lead to instant death. Therefore this is the clinical importance of this cerebellar tonsil. There is a condition called tethered chord syndrome or phylum terminal syndrome where the phylum terminal is a short stout thick chord which is attached to the coccyx and therefore it exerts traction on the cervical medullary junction as a result of which the medulla can be herniated through the foremen magnum. There are also some congenital conditions called carry type 1 and carry type 2 or Arnold carry malformation where the cerebellar vermis can herniate through the foremen magnum as we can see in the company's journal MRI views. This is a t1 MRI of a child showing herniation of the cerebellar vermis and the medulla through the foremen magnum and this is another t2 MRI of another Arnold carry malformation showing herniation of the cerebellar vermis through the foremen magnum. Next thing we will draw your attention to are these arteries that we can see here one on either side on the under surface of the cerebellar hemisphere and we can see the other one on the left side here. These are the branches of the vertebral artery respectively on the left and the right side which are referred to as the posterior inferior cerebellar artery or PICA in short. This posterior cerebellar artery it supplies the inferior surface of the cerebellum posterior part as well as the lateral part of the medulla which is deep inside which you cannot see in this dissection. This artery is a very important artery because occlusion of this artery can produce what is known as the PICA syndrome or the lateral medullary syndrome. It is also referred to as Wallenberg syndrome. So these are a few points which I want to mention in this suboxial triangle and the cervical medullary junction. Thank you very much for watching Dr. Sanjay Sanyal signing out. If you have any questions or comments please put them in the comment section below. Please like and subscribe. Have a nice day.